1. Field of the Invention
The present invention relates to an optical pickup device and an optical disk drive using the same. More specifically, the present invention relates to an optical pickup device for an optical disk drive which focuses a light beam to a corresponding one of two optical disks of different types for recording of information, and receives a reflected light beam from the corresponding optical disk for reproduction of information.
2. Description of the Related Art
In the optical disk drive, storage media, such as optical disks, in which tracks in the spiral or concentric formation are formed in the recording surface of the optical disk, are used for recording and reproduction of information. The optical disk drive emits a light beam to the optical disk to record information in the recording surface of the optical disk, and receives a reflected light beam from the recording surface of the optical disk to reproduce the information based on the received light beam.
The optical disk drive is usually equipped with an optical pickup device. The optical pickup device is provided for emitting a laser beam to the recording surface of an optical disk to form a small light spot thereon, and for receiving a reflected laser beam from the recording surface of the optical disk.
The optical pickup device usually includes an object lens, an optical system and a photodetector. The optical system is provided to lead the light beam emitted by the light source, to the recording surface of the optical disk, and to lead the return light beam reflected from the recording surface of the optical disk to a predetermined light-receiving location where the photodetector is arranged.
In response to the received light beam, the photodetector outputs the electrical signal indicating the reproduced information of data that is recorded in the optical disk. Also, the optical pickup device outputs the signal including information (servo control information) required for the position control of the optical pickup device itself and the object lens.
In recent years, a DVD (digital versatile disk) has been generalized as a mass storage medium having a recording capacity much larger than that of a CD (compact disk).
In order to perform recording and reproduction to CD, the laser light having the wavelength 780 nm is used. In order to perform recording and reproduction to DVD, the laser light having the wavelength 650 nm is used.
For this reason, the optical disk drive for CD and the optical disk drive for DVD have been developed respectively as different peripheral devices of information processing devices, such as personal computer.
With recent developments of small-sized, lightweight information processing devices, the necessity for the optical disk drive, which can access both CD and DVD, is increasing.
In this case, in order to access both DVD and CD, the optical pickup device must be provided with a light source unit containing both the semiconductor laser (DVD light source) which outputs the laser light whose wavelength is 650 nm, and the semiconductor laser (CD light source) which outputs the laser light whose wavelength is 780 nm. Furthermore, the optical pickup device must be provided with the optical system for detecting each of the two laser beams output from the two light sources.
However, if the optical system for 650 nm and the optical system for 780 nm are arranged individually in the optical pickup device, the problem that the size of the optical pickup device is enlarged arises.
In the following the optical pickup device equipped with the light sources of two different wavelengths will be called the two-wavelength optical pickup device.
For example, Japanese Patent No. 3026279 discloses a laser module for a recording/reproduction apparatus. This laser module is equipped with an LD module in which two laser components which output laser light beams having different wavelengths are integrated. In the laser module, a light-receiving component is commonized to receive both the return light beams of the different wavelengths.
According to the optical pickup device using the laser module, the commonization of the optical system and the reduction of the number of the optical parts needed are possible, and simplification of the assembly of the components, the reduction in cost, and the miniaturization of the device are promoted.
FIG. 17 shows a relationship between the intensity distribution of the light beam output from the semiconductor laser and the location of the activation layer thereof.
Generally, the light beam (the outgoing light beam) output from the semiconductor laser that is used as a light source is a divergent light beam with the intensity distribution in the form of an ellipse having the major axis whose direction accords with the direction perpendicular to the surface of the activation layer (hetero-junction plane) AL of the semiconductor laser LD, as shown in FIG. 17.
The rate of the light beam received by the object lens and focused on the recording surface of the optical disk (which light beam is called the received light beam) over the outgoing light beam of the light source is represented by the ratio of the minimum optical intensity in the received light beam to the optical intensity in the center of the outgoing light beam. This ratio is called the rim intensity (RIM).
FIG. 18 shows an example of the intensity distribution of the received light beam in the case of RIM=50%.
FIG. 19 shows a relationship between the optical efficiency and the rim intensity of the light beam output from the semiconductor laser. The optical efficiency, which is indicated by the ratio of the quantity of light on the optical disk recording surface to the quantity of light in the outgoing light beam, is almost in the inverse proportion with the RIM, as shown in FIG. 19.
If the optical pickup device is designed to raise the RIM, the optical efficiency will fall. If the optical pickup device is designed to raise the optical efficiency, the RIM will become low.
Usually, the optical pickup device is designed so that the RIM to the outgoing light beam of CD light source is lower than the RIM to the outgoing light beam of DVD light source.
This is because it is necessary to control accurately the diameter of a light spot on the recording surface of DVD, as the recording density of DVD is higher than that of CD. On the other hand, importance is attached to raising the optical efficiency for CD light source.
However, in the optical pickup device using the laser module of Japanese Patent No. 3026279, the RIM to the outgoing light beam of CD light source and the RIM to the outgoing light beam of DVD light source become almost equal.
When the optical system is optimized to DVD, the optical efficiency of CD light source falls, and it is difficult to deal with improvement in the access speed for the optical disk. On the other hand, when the optical system is optimized to CD, the problem arises that it is difficult to control accurately the diameter of a light spot on the recording surface of DVD.